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SFS Annual Meeting

Thursday, June 6, 2024
10:30 - 12:00

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C25 Food Webs

10:30 - 10:45 | Independence Ballroom D | GLOBAL PATTERNS OF ALLOCHTHONY IN STREAM-RIPARIAN META-ECOSYSTEMS

6/06/2024  |   10:30 - 10:45   |  Independence Ballroom D

Global patterns of allochthony in stream-riparian meta-ecosystems Ecosystems that are coupled by reciprocal flows of energy and nutrient subsidies can be viewed as a single “meta-ecosystem”. Despite these connections, the reciprocal flow of subsidies is greatly asymmetrical and seasonally pulsed. Here, we synthesize existing literature on stream-riparian meta-ecosystems to quantify global patterns of the amount of subsidy consumption by organisms, known as “allochthony.” These resource flows are important since they can comprise a large portion of consumer diets but can be disrupted by human modification of streams and riparian zones. Despite the known asymmetrical subsidy flows, we found stream and riparian consumer allochthony to be equivalent. Although both fish and stream invertebrates rely on seasonally pulsed allochthonous resources, we find allochthony varies seasonally only for fish, being nearly greater during summer and fall than the winter and spring. We also find that consumer allochthony varies with feeding traits for aquatic invertebrates, fish, and terrestrial arthropods, but not for terrestrial vertebrates. Finally, we find that allochthony varies by climate for aquatic invertebrates, being nearly twice as great in arid than tropical climates, but not for fish. These findings are critical to understanding the consequences of global change, as ecosystem connections are being increasingly disrupted.

Daniel Allen (Primary Presenter/Author), Penn State, daniel.c.allen@psu.edu;

James Larson (Co-Presenter/Co-Author), U.S. Geological Survey, jhlarson@usgs.gov;

Christina A. Murphy (Co-Presenter/Co-Author), U.S. Geological Survey, Maine Cooperative Fish and Wildlife Research Unit, Orono, ME, christina.murphy@maine.edu;

Erica Garcia (Co-Presenter/Co-Author), Charles Darwin University, erica.garcia@cdu.edu.au;

Kurt Anderson (Co-Presenter/Co-Author), University of California, Riverside, kurt.anderson@ucr.edu;

Michelle Busch (Co-Presenter/Co-Author), University of Kansas, m.h.busch@ku.edu;

Alba Argerich (Co-Presenter/Co-Author), University of Missouri-Columbia, argericha@missouri.edu;

Alice Belskis (Co-Presenter/Co-Author), New Jersey Department of Environmental Protection, albelskis@gmail.com;

Kierstyn Higgins (Co-Presenter/Co-Author), The Pennsylvania State University, kth5285@psu.edu;

Brooke Penaluna (Co-Presenter/Co-Author), PNW Research Station, US Forest Service, brooke.penaluna@oregonstate.edu;

Veronica Saenz (Co-Presenter/Co-Author), Penn State, vks5352@psu.edu;

Jay Jones (Co-Presenter/Co-Author), U. of Alaska, Jay.Jones@alaska.edu;

Matt Whiles (Co-Presenter/Co-Author), University of Florida, mwhiles@ufl.edu;

10:45 - 11:00 | Independence Ballroom D | HOUSTON, WE HAVE A PROBLEM. BURROWING MAYFLIES IN AIRSPACE: USING WEATHER RADAR TO UNDERSTAND POPULATION CHANGES OVER TIME AND ACROSS ECOSYSTEMS

6/06/2024  |   10:45 - 11:00   |  Independence Ballroom D

Houston, we have a problem. Burrowing mayflies in airspace: Using weather radar to understand population changes over time and across ecosystems Documentation of insect declines have been publicized, but in fact abundances are often variably affected by environmental change. The reason for, and the extent of, threats across >1 million species coupled with varying patterns of environmental change makes predicting declines difficult. Recent radar technology provides a tool to track large-scale changes in insect movement, and more recently, for production. Weather radar technology has advanced so that insects that fly above 300m can be detected. Some adult aquatic insects move at high altitude making their emergence and movement across the landscape quantifiable and predictable based on common properties like temperature, barometric pressure and wind speed. We predicted that burrowing mayfly emergence could be detected, quantified and linked to biophysical characteristics like degree days and wind speed. We also hypothesized that mayfly secondary production via benthic sampling would correspond with ~25% of the total mayfly biomass quantified using weather radar at the same site. We were able to detect, quantify and then predict mayfly emergence from Lake Seminole, but variation in the cohort structure and 2 -week lag time from emergence to airspace increased the uncertainty of aquatic to radar relationships. These results contrast with the more synchronous mayflies in the Great Lakes and Upper Mississippi basin. We will present approaches, challenges and applications of radar-aquatic insect tracking to understand insect population changes across large spatial scales. We are optimistic that radar technology can be used as a supplemental tool for tracking and identifying causes and consequences of aquatic insect declines.

Sally Entrekin (Primary Presenter/Author), Virginia Tech, sallye@vt.edu;

Chelsea Smith (Co-Presenter/Co-Author), University of Alabama, chelsea.smith@jonesctr.org;

Stephen Golladay (Co-Presenter/Co-Author), Georgia Water Planning and Policy Center at ASU, steve.golladay@jonesctr.org;

Jennifer L. Tank (Co-Presenter/Co-Author), University of Notre Dame, jtank@nd.edu;

Dominic Chaloner (Co-Presenter/Co-Author), University of Notre Dame, dchaloner@nd.edu;

Phillip Stepanian (Co-Presenter/Co-Author), Lincoln Laboratory, Massachusetts Institute of Technology, phillip.stepanian@gmail.com;

11:00 - 11:15 | Independence Ballroom D | STABLE ISOTOPES FAIL TO ACCURATELY REFLECT A HIGH CARBOHYDRATE DIET.

6/06/2024  |   11:00 - 11:15   |  Independence Ballroom D

Stable Isotopes Fail to Accurately Reflect a High Carbohydrate Diet. Positive interactions among invasive species have the potential to increase the biomass of one or both species and enhance their impact on native ecosystem function. Previous studies indicate that fruits from non-native riparian trees (Russian olive; Elaeagnus angustifolia) provide a trophic subsidy to channel catfish (Ictalurus punctatus) populations in rivers where they co-occur. Russian olive fruits are a unique diet item due to its high carbohydrate and low lipid structure. Feed trials indicate that olive fruits provide a source of metabolic energy to channel catfish but fail to provide sufficient nutrition for somatic growth. Although previous diet studies indicate that olives are an important energy source for channel catfish, stable isotope signatures appear to underestimate their contribution to catfish diets. The objective of this study is to 1) determine the contribution of olive fruit in the diet to stable isotope signatures of muscle and fin tissue of channel catfish, and 2) evaluate the performance of isotope mixing models for predicting catfish diets when fed a high energy diet of olive fruit. Indications show that the major diet item by occurrence Russian olive is not showing a signature in muscle tissue. These interactions may also involve frugivory, further shaping the dynamics within the invaded ecosystem. Our results indicate that isotope signatures may not accurately reflect fish diets when fed high carbohydrate diets.

Justin Sturtz (Primary Presenter/Author), South Dakota State University, justin.sturtz@sdstate.edu;

Christopher Cheek (Co-Presenter/Co-Author), Purdue University, Christopher.Cheek@sdstate.edu;

11:15 - 11:30 | Independence Ballroom D | RESPONSES OF MACROPHYTES AND CRAYFISH TO EXPERIMENTAL WET SEASON DEPTH RESTRICTION IN A SUBTROPICAL WETLAND

6/06/2024  |   11:15 - 11:30   |  Independence Ballroom D

RESPONSES OF MACROPHYTES AND CRAYFISH TO EXPERIMENTAL WET SEASON DEPTH RESTRICTION IN A SUBTROPICAL WETLAND Natural and managed water depth variation impacts population dynamics and vegetated habitats within wetland ecosystems. While hydrological drought (seasonal drying) mediates trophic dynamics in wetlands by reducing the impacts of aquatic predators like fish, the impact of short-term and long-term differences in depth during flooded seasons is less clear. We conducted a five-year study in which we experimentally manipulated water depth in four 8-ha replicate wetlands of the central Everglades, during the wet season. Two wetlands experienced a shallow hydro-pattern in which maximum depths were limited and two wetlands were flooded to deeper depths according to available natural rainfall patterns. We controlled water depth independent of hydrological drought (i.e., equalizing hydroperiod) by maintaining all wetlands in a flooded condition during the dry season. Crayfish (Procambarus fallax) abundances and macrophyte densities responded in expected ways with wetlands under the shallow treatment experiencing elevated crayfish abundances and increased wet season stem densities after five years. Abundances of small marsh fishes (mostly Poeciliidae and Fundulidae), and large-bodied predatory fishes (mostly Centrarchidae and Cichlidae) did not differ significantly after five years. The faunal effects observed indicate that vegetation structure may be an important component affecting population dynamics and food web structure in addition to the previously established importance of hydrological drought that temporarily reduces fish populations. Short-term hydrologic manipulations would not capture this community change as it seems to have been mediated by vegetation changes that strengthened after three years.

Jeffrey Sommer (Primary Presenter/Author), Florida International University, jsommer@fiu.edu;

Mark Cook (Co-Presenter/Co-Author), South Florida Water Management District, Mcook@sfwmd.gov;

Eric Cline (Co-Presenter/Co-Author), South Florida Water Management District, Ecline@sfwmd.gov;

Nathan Dorn (Co-Presenter/Co-Author), Florida International University, ndorn@fiu.edu;

11:30 - 11:45 | Independence Ballroom D | INFLUENCE OF NETWORK POSITION ON FOOD CHAIN LENGTH IN RIVERS

6/06/2024  |   11:30 - 11:45   |  Independence Ballroom D

INFLUENCE OF NETWORK POSITION ON FOOD CHAIN LENGTH IN RIVERS Food chain length (FCL) is an important property of ecological communities; FCL influences community structure, energy flow, and concentration of contaminants in top predators, many of which humans consume. Much of previous empirical studies on FCL have been conducted in simple two-dimensional lentic and oceanic systems, and ecosystem size has been hypothesized as one of the major determinants of FCL. However, there is a dearth of studies on FCL in complex branching ecosystems, where the application of simplified two-dimensional representation may be inappropriate. Riverine systems form complex branching networks, with a diversity of tributaries that support habitat heterogeneity. The central habitats within a network may support longer food chains through consistent immigration from a diversity of connected habitats (the Network Position Hypothesis or NPH). Here, we conducted a meta-analyses of stable isotope data from the US rivers to test the NPH. We used the betweenness as a measure of network centrality, which measures the fraction of river segments that pass through a specific river segment in the dendritic network. We predict that FCL increases with increasing betweenness due to increased immigration from connected habitats. Our research will shed lights on the overlooked role of network position in complex networks in dictating FCL.

Timothy Lee (Primary Presenter/Author), University of North Carolina at Greensboro, tslee@uncg.edu;

Akira Terui (Co-Presenter/Co-Author), Department of Biology, University of North Carolina at Greensboro, hanabi0111@gmail.com;

11:45 - 12:00 | Independence Ballroom D | RIVER NETWORK COMPLEXITY AND FOOD CHAINS: THEORY AND A GLOBAL SYNTHESIS

6/06/2024  |   11:45 - 12:00   |  Independence Ballroom D

River network complexity and food chains: theory and a global synthesis Understanding the determinants of food chain length in natural ecosystems is a central question in ecology. Hypothetical controls include productivity, disturbance regime, and ecosystem size. However, existing theories often assume simplistic, two-dimensional habitat structures. This may limit their ability to accurately predict food chain length in ecosystems with complex, branching architectures. In this study, we merge theoretical frameworks with a global synthesis of stable isotope data to show that network complexity emerges as a primary driver of food chain length in branching river networks. To this end, we constructed a predator-prey model consisting of 16 trophic species, which serves as a local food web within branching networks. This spatial food web model predicted independent, positive influences of both ecosystem size and network complexity (indicated by branching probability) on food chain length. We tested this theoretical prediction through a cross-continental meta-analysis of stable isotopes. We confirmed a robust positive correlation between food chain length and network complexity. However, the impact of ecosystem size (watershed area) on food chain length appears weak and variable. These findings underscore the significance of network complexity as an often overlooked yet prevalent driver of food chain length in branching ecosystems.

Akira Terui (Primary Presenter/Author), Department of Biology, University of North Carolina at Greensboro, hanabi0111@gmail.com;

Shota Shibasaki (Co-Presenter/Co-Author), National Institute of Genetics, shibasaki.sh@gmail.com;

Jacques Finlay (Co-Presenter/Co-Author), University of Minnesota, jfinlay@umn.edu;